SECT. 9] 



PROTEIN METABOLISM 



1073 



O Total non-protei 



O " » " " (Nakamura) 



<5 Non-protein nitrogen precipibabie with 

 phosphotungsbic acid (Nalomura)^ 



<^ Non-protein nitrogen not pre- 

 cipitable with phosphotung- 

 sbic acid(Nakar 



the absorption intensity for protein is falling rapidly and that for 

 fatty substances is rising rapidly. On the other hand, it is known 

 that the contents of the albumen-sac tend to be included in the yolk 

 at the end of development, about the time of the opening of the 

 sero-amniotic duct, and this may partly explain Riddle's results. 

 Riddle also investigated the protein content of the yolk-sac itself 

 from the 12th day onwards, finding practically no change, and 

 obtained various figures for the 



solid central core of yolk, the O Total non-protein n.trogen(Needham) 



more Hquid part, and the yolk 

 enclosed in the walls of the sac. 

 These are given on the graph, 

 but, as they are somewhat erratic 

 and depend on an arbitrary 

 selection of the material, they 

 are not so important as the rest. 

 These viscous bodies in the 

 central core, which differed very 

 markedly in chemical composi- 

 tion, were explained by Riddle 

 as being in one case unaltered 

 yolk from the beginning of de- 

 velopment, and in the other case 

 a clump of egg-white driven into 

 the yolk and imperfectly in- 

 filtrated with it. Riddle also 

 found that, when yolk is being 

 resorbed in the hen by the follicle 

 which secreted it, there is a more rapid removal of Hpoids than of fats, 

 and of fats than of proteins. 



It will have been remarked that, so far, nothing has been said about 

 the non-protein nitrogen within the embryo. The early work of 

 Demant on human and guinea-pig foetuses, in which a high con- 

 centration of peptones and albumoses was found, was discredited 

 by Neumeister. In 1927 Needham estimated the nitrogen in the 

 trichloracetic filtrate by Rose's modification of the Kjeldahl method. 

 The curve obtained was regular (Fig. 309), but more interesting 

 points were brought out by the expression of the non-protein nitrogen 

 of the embryo in terms of wet weight. Fig. 310 shows this, together 



Days 



Fig. 310. 



